Loudspeaker system comprising equalization dependent on volume control

ABSTRACT

The application relates to a loudspeaker system including an input unit providing an electric input audio signal; an equalization unit for modifying said electric input audio signal in dependence on frequency and to provide an equalized electric audio signal according to a predefined equalization function, a loudspeaker unit for converting said equalized electric audio signal to an acoustic output sound signal, and a user interface for modifying a volume level of said output sound signal in a multitude (N) of steps V 0 , V 1 , . . . , V N . The application further relates to a method communication device comprising the loudspeaker system and to its use. The present application provides an improved loudspeaker system in which the equalization unit is configured to apply a specific equalization function EQ 0 , EQ 1 , . . . , EQ N  to the electric input audio signal in each of said multitude of steps V 0 , V 1 , . . . , V N  of the volume level.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of co-pending application Ser. No.14/173,651, filed on Feb. 5, 2014, all of which is hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD

The present application relates to loudspeaker systems, e.g. suchsystems that work under power constraints. The disclosure relatesspecifically to a loudspeaker system comprising a loudspeaker unit, anequalization unit, and a user interface.

The application furthermore relates to a communication device comprisingthe loudspeaker system and to the use of the loudspeaker system.

Embodiments of the disclosure may e.g. be useful in applications such ashandsfree telephone systems, mobile telephones, teleconferencing systems(e.g. speakerphones), public address systems, karaoke systems, classroomamplification systems, etc.

BACKGROUND

Typically, a loudspeaker unit exhibits a low frequency fall-off in itsfrequency transfer function. In audio systems, it is known to boost lowfrequencies by having the option of applying a fixed dedicated ‘extragain’ at low frequencies (‘Loudness’ button). WO9318626A1 describesdynamic adjustment of low frequency gain, where the applied gain isdependent on the content (magnitude) of signal components at lowfrequencies in the current signal.

SUMMARY

The present application presents an alternative strategy for improvingsound reproduction of a broadband signal at low frequencies or at otherfrequencies where a loudspeaker unit exhibits deficiencies (e.g. atrelatively high frequencies or at intermediate frequencies, where aparticular loudspeaker unit or type of loudspeaker has a substantialdeviation in its otherwise flat frequency transfer function).

An object of the present application is to provide an improveloudspeaker system.

Objects of the application are achieved by the invention described inthe accompanying claims and as described in the following.

A Loudspeaker System:

In an aspect of the present application, an object of the application isachieved by a loudspeaker system comprising

an input unit providing an electric input audio signal;

an equalization unit for modifying said electric input audio signal or aprocessed version thereof in dependence on frequency and to provide anequalized electric audio signal according to a predefined equalizationfunction,

a loudspeaker unit for converting said equalized electric audio signalor a processed version thereof to an acoustic output sound signal, and

a user interface for modifying a volume level of said output soundsignal in a multitude of steps V₀, V₁, . . . , V_(N), wherein theequalization unit is configured to apply a specific equalizationfunction EQ₀, EQ₁, . . . , EQ_(N) to the electric input audio signal ineach of said multitude of steps V₀, V₁, . . . , V_(N) of the volumelevel.

This has the advantage of allowing an equalization to be adapted to aspecific user selected volume level of the loudspeaker unit.

In an embodiment, the equalization unit is configured to provide that atleast two, or a majority, or all, of said specific equalizationfunctions EQ₀, EQ₁, . . . , EQ_(N) are different.

In an embodiment, the equalization unit is configured to provide thateach specific equalization function defines a frequency dependentattenuation of the electric input audio signal.

In an embodiment, each specific equalization function defines a lowfrequency threshold frequency f₂, and a high frequency thresholdfrequency f₃, defining respective low, medium and high frequencyregions, wherein the attenuation in the medium frequency region betweensaid low frequency and high frequency threshold frequencies is largerthan the attenuation in the low frequency region below said lowfrequency threshold frequency.

In an embodiment, the loudspeaker system is configured to provide

-   -   that each specific equalization function EQ_(i), i=0, 1, 2, . .        . , N, is applied to the electric audio signal when the        corresponding respective step V_(i), i=0, 1, 2, . . . , N, of        the volume level is selected, where increasing i corresponds to        increasing volume,    -   that each equalization function EQ_(i)(f) represents a specific        frequency dependent attenuation EQ_(i)(f), and    -   that the attenuation of an equalization function EQ_(i)(f) is        smaller than the attenuation of an equalization function        EQ_(j)(f) for all frequencies in the range from an LF frequency        f_(LF) to a HF frequency f_(HF), if i is larger than j.

In an embodiment, the LF frequency f_(LF) is smaller than the lowfrequency threshold frequency f₂. In an embodiment, the HF frequencyf_(HF) is larger than the high frequency threshold frequency f₃. In anembodiment, the loudspeaker system is configured to operate in an audiofrequency range between a minimum frequency f_(min) and a maximumfrequency f_(max). In an embodiment, minimum frequency f_(min) issmaller than 100 Hz, such as smaller than 50 Hz. In an embodiment, themaximum frequency f_(max) is larger than 4 kHz, e.g. larger than 8 kHz.Hence, in an embodiment, f_(min)≦f_(LF)<f₂, and f₃<f_(HF)≦f_(max).

A typical loudspeaker unit has a medium frequency where a substantiallyflat transfer function H(f) for frequencies in the medium frequencyrange between first (f_(LFcut)) and second (f_(HFcut)) frequencies(f_(LFcut)<f_(HFcut)) can be provided. Below a low frequency cut-offfrequency (f_(LFcut)), the frequency response of the loudspeaker unitrolls off. In other words, the loudspeaker unit will—other things beingequal—play low frequency sounds (below f_(LFcut)) at a lower outputlevel than sounds in the medium frequency range. The same is to acertain extent true for sound signals above a high frequency cut-offfrequency (f_(HFcut)). These cut-off frequencies are dependent on theloudspeaker type, size, etc. In an embodiment, the low frequency cut-offfrequency (f_(LFcut)) is smaller than 500 Hz, or smaller than 400 Hz,e.g. in the range from 200 Hz to 400 Hz. In an embodiment, the highfrequency cut-off frequency (f_(HFcut)) is larger than 4 kHz, e.g.larger than 8 kHz, e.g. larger than 12 kHz, e.g. in the range from 4 kHzto 10 kHz.

In an embodiment, the loudspeaker system is configured to provide thatthe low frequency threshold frequency f₂ of a specific equalizationfunction is dependent on a low frequency cut-off frequency f_(LFcut) ofthe loudspeaker unit. In an embodiment, the low frequency thresholdfrequency f₂(i) of each specific equalization function EQ_(i)(f), i=0,1, 2, . . . , N, are within 50 Hz of each other, or within 25 Hz of aneighboring equalization function (EQ_(i+1)(f) or EQ_(i−1)(f)). In anembodiment, the low frequency threshold frequency f₂(i) of each specificequalization function EQ_(i)(f), i=0, 1, 2, . . . , N, are equal. In anembodiment, an average of the individual specific equalization functionEQ_(i)(f), i=0, 1, 2, . . . , N, is (essentially) equal a low frequencycut-off frequency (f_(LFcut)) of the loudspeaker unit. In an embodiment,the low frequency threshold frequency f₂(i) of each specificequalization function EQ_(i)(f), i=0, 1, 2, . . . , N, are equal andequal to the low frequency cut-off frequency (f_(LFcut)) of theloudspeaker unit. The same relations can be assumed to exist betweenf₃(i) of each specific equalization function EQ_(i)(f), i=0, 1, 2, . . ., N and the high frequency cut-off frequency (f_(HFcut)) of theloudspeaker unit.

In an embodiment, a specific equalization function is implemented by afilter, e.g. an RR (Infinite Impulse response) filter, e.g. an analoguefilter or a digital IIR filter. In a specific embodiment, theequalization function is implemented by a digital filter, e.g. a digitalFIR (Finite Impulse Response) filter. In a preferred embodiment, theequalization function is implemented by a digital IIR filter, e.g. usingone or more biquad filters (whose transfer function can be written as aratio of two quadratic functions (a second order feed-forward and asecond order feedback filter function). Various aspects of filters, inparticular adaptive filters are e.g. described in [Haykin; 2001].

In an embodiment, the loudspeaker system comprises a memory whereinpredefined sets of filter coefficients for implementing (e.g.approximating) specific equalization functions are stored. In anembodiment, a specific set of filter coefficients (b_(ip), a_(iq))corresponding to a specific equalization function EQ_(i) is applied tothe filter (e.g. a digital IIR filter) when a specific volume levelV_(i) is selected via the user interface.

In an embodiment, the multitude of steps V₀, V₁, . . . , V_(N) of thevolume level comprises at least two steps, such as at least 3 steps(N≧2), such as at least 5 steps (N≧4), such as at least 7 steps (N≧6).

In an embodiment, the loudspeaker system is configured to operate in afixed mode. In an embodiment, the loudspeaker system is configured tooperate in two or more modes. In an embodiment, the loudspeaker systemis configured to operate in two or more modes, wherein each mode has aseparate set of volume dependent equalization functions.

In an embodiment, the loudspeaker system is configured to operate in atleast two modes of operation, a first mode and a second mode. In anembodiment, the first mode is a full bandwidth mode, wherein areproduction of music or other broadband audio signal (in a high qualityconsidering the system constraints) is aimed at. In an embodiment, thesecond mode is a limited bandwidth mode, wherein a reproduction a speechor other limited bandwidth audio signal (e.g. a telephone signal) isaimed at. In an embodiment, a mode of operation may be defined orinfluenced by the current power supply (different equalization functionsbeing e.g. defined for a relatively lower supply voltage (e.g. from abattery) than for a relatively higher supply voltage (e.g. from a mainssupply or from a separate device, e.g. via an (e.g. audio) interface).In an embodiment, separate modes of operation (having their specificvolume dependent equalization functions) may be defined by the currentlyconnected type of device, a mobile telephone, a headset, a PC, etc.

In an embodiment, when the loudspeaker system is in the first, fullbandwidth mode, each specific equalization function EQ_(i), i=0, 1, 2, .. . , N, decreases its attenuation from a maximum attenuation valueL(f₂) in the intermediate frequency range (at a low frequency thresholdfrequency f₂) to a minimum attenuation value (L(f₁), e.g. equal to 0) ata first lower frequency f₁ (f₁<f₂) (see e.g. FIG. 3). In an embodiment,the decrease in attenuation from L(f₂) to L(f₁) is approximately linearon a logarithmic scale. In an embodiment, the first lower frequency f₁is essentially equal for all specific equalization functions EQ_(i),i=0, 1, 2, . . . , N. In an embodiment, the first lower frequency f₁ isdifferent for at least some of the specific equalization functionsEQ_(i), i=0, 1, 2, . . . , N.

In an embodiment, the loudspeaker system is configured to allow acurrent mode of operation to be changed (e.g. overriding an automaticmode selection) via the user interface. In an embodiment, the userinterface comprises an activation element, e.g. a button or a selectionwheel. In an embodiment, the user interface comprises a touch sensitivedisplay. In an embodiment, the user interface is implemented in a remotecontrol device via a communication interface. In an embodiment, theremote control device comprises a PC or a cellular phone, e.g. aSmartPhone. In an embodiment, the user interface is implemented as anAPP on a SmartPhone.

In an embodiment, the loudspeaker system work under power constraints.The maximum voltage swing that can be applied to the loudspeaker unitcan e.g. be limited by available power in the loudspeaker system (be itsupplied by another device or a local energy source), by a maximumamplifier output, by a specifications of the loudspeaker unit (e.g. amaximum displacement restriction, and/or a maximum power input orrating). In an embodiment, the loudspeaker system is configured to workunder power constraints in that the maximum voltage swing that can beapplied to the loudspeaker unit is limited by one or more of thefollowing a) the available power in the loudspeaker system, b) a maximumamplifier output, and c) specifications of the loudspeaker unit.

In an embodiment, the loudspeaker system is energized by a power sourceproviding a limited maximum voltage swing of the audio signal beingprocessed by the loudspeaker system (e.g. the electric input audiosignal received from another device or from another part of theloudspeaker system, or the electric output audio signal fed to theloudspeaker unit). In an embodiment, the loudspeaker system is energizedfrom another device or system (e.g. a PC or a cell phone or anotherentertainment device), e.g. via a cable connection, e.g. comprising aUSB (Universal Serial Bus) interface (or via a wireless connectionsimultaneously providing power to the loudspeaker system). In anembodiment, the maximum voltage of the audio interface is smaller thanor equal to 5 V. In an embodiment, the maximum draw of current via theaudio interface is smaller than or equal to 500 mA. In an embodiment,the loudspeaker system comprises a local energy source, e.g. a battery,such as a rechargeable battery (e.g. a NiMH or a Li-Ion or a Li-Polymerbattery) or a non-rechargeable (conventional) battery, for energizingcomponents of the loudspeaker system for a certain amount of time. In anembodiment, a maximum voltage of the battery is smaller than 4 V.

In an embodiment, the loudspeaker unit has a maximum dimension that issmaller than or equal to 1 m, such as smaller than or equal to 0.5 m,such as smaller than or equal to 0.2 m, or smaller than or equal to 0.15m, e.g. of the order of 0.1 m or less, e.g. in the range from 0.002 m to0.1 m.

In an embodiment, the loudspeaker unit has a maximum power rating (peakpower) indicative of the maximum power that can be applied to theloudspeaker without damage (or substantial distortion) smaller than orequal to 30 W, such as smaller than or equal to 15 W, such as smallerthan or equal to 5 W, such as smaller than or equal to 2 W.

In an embodiment, the loudspeaker system comprises a (wired or wireless)audio interface to another device. In an embodiment, the loudspeakersystem comprises a multitude of (wired or wireless) audio interfaces toother devices (such other devices being capable of receiving (sinking)and/or transmitting/forwarding (sourcing) audio signals. In anembodiment, ‘other devices’ comprise e.g. a wireless telephone (e.g. acellphone, such as a Smartphone), a computer (e.g. a PC), a headset, ahearing instrument, etc. In an embodiment, the loudspeaker systemcomprises at least two (wired or wireless) audio interfaces. In anembodiment, the loudspeaker system comprises at least one wired audiointerface (comprising (a cable and) an electric connector, e.g. anytelephone jack, an USB connector (e.g. standard or mini or micro USBconnectors), a phone connector, an audio jack connector, etc.). In anembodiment, the loudspeaker system comprises at least one wireless audiointerface (e.g. based on Bluetooth, e.g. Bluetooth Low Energy, DECT,ZigBee, or other proprietary or standardized audio interfaces).

In an embodiment, the loudspeaker system comprises at least one (audio)interface to a (switched) network (e.g. to a fixed landline telephoneconnection to the PSTN (Public Switched Telephone Network) or to theInternet (e.g. for establishing Internet telephony based on digitalpacket switched VoIP connections)) capable of exchanging audio signalsbetween the loudspeaker system and another communication device, such asat least two, such as two or more audio network interfaces. In anembodiment, the loudspeaker system is configured to be connected to acomputer (e.g. a PC or tablet, e.g. via a USB interface) comprising asoftphone, i.e. which is adapted to run software for establishing atelephone connection to a switched network (e.g. to the PSTN). In anembodiment, the loudspeaker system is configured to be connected to aheadset or a wireless phone/cellular phone (e.g. a SmartPhone, e.g. viaa phone connector (audio jack) adapted for allowing two-way exchange ofaudio data between the loudspeaker system and the other device forsourcing and sinking audio signals).

In an embodiment, the loudspeaker system is configured to automaticallybe energized by another device or system, when connected to such otherdevice or system via an audio interface providing power. In anembodiment, the loudspeaker system is configured to automatically beenergized by the local energy source when the loudspeaker system is NOTconnected to a device or system via an audio interface providing power.

In an embodiment, the loudspeaker system is configured to automaticallybe brought in a particular mode of operation depending on the currentlyconnected audio interfaces. In an embodiment, the loudspeaker system isconfigured to be brought in the second (limited band) mode of operationwhen a (incoming or outgoing) telephone connection via an audiointerface of the loudspeaker system is detected. In an embodiment, theloudspeaker system comprises an I/O control unit adapted to monitor thecurrently connected interface(s) (connectors) and possibly signals ofthe interface(s)). In an embodiment, the loudspeaker system isconfigured to be brought in the first (broadband) mode of operation whenNOT in the second (limited band) mode of operation. In an embodiment,the loudspeaker system is configured to allow a current mode ofoperation to be changed (e.g. overriding an automatic mode selection)via the user interface.

The loudspeaker unit can be of any kind, e.g. a dynamic loudspeaker(using a permanent magnet and a (voice) coil connected to a diaphragm orcone; the coil (and hence the diaphragm) is axially moving in the fieldfrom the permanent magnet when an electric current of varying polarity(AC) is applied to the coil). Other loudspeaker types, e.g. based onpiezoelectric or electrostatic principles, etc., can be used. Thechamber surrounding the loudspeaker unit can be open or closed. Varioustypes of acoustic couplings (drivers and acoustic resonators andtransmission paths) of the loudspeaker unit and a surrounding chambercan be used, e.g. band pass, bass reflex, horn, etc.

In an embodiment, the loudspeaker system comprises a multitude ofloudspeakers, e.g. two or more.

In an embodiment, the loudspeaker system further comprises a side bandcompressor unit (as e.g. described in WO9318626A1) for dynamicallyboosting a low frequency range in dependence of the present content(e.g. energy or power spectral density) in that frequency range, e.g. sothat low frequency content is amplified to a lesser extent, the largerthe low frequency content at a given point in time.

In an embodiment, the loudspeaker system further comprises a loudnessequalization unit configured to compensate for psychoacousticdifferences in the perception of a given sound pressure level overfrequency (when possible).

A Communication Device:

A communication device comprising a loudspeaker system as describedabove in the detailed description of embodiments, in the drawings and inthe claims is furthermore provided.

In an embodiment, the communication device comprises

-   -   a first microphone signal path comprising        -   a microphone unit,        -   a first signal processing unit, and        -   a transmitter unit            -   said units being operationally connected to each other                and configured to transmit a processed signal                originating from an input sound picked up by the                microphone, and    -   a second loudspeaker signal path comprising        -   a receiver unit,        -   a second signal processing unit, and        -   a loudspeaker unit operationally            -   said units being operationally connected to each other                and configured to provide an acoustic sound signal                originating from a signal received by the receiver unit.

Thereby a speakerphone comprising a loudspeaker system according to thepresent disclosure can be implemented.

In an embodiment, the communication device comprises at least one audiointerface to a switched network and at least one audio interface to anaudio delivery device. In an embodiment, the (one way) audio deliverydevice is a music player or any other entertainment device providing anaudio signal. In an embodiment, the (loudspeaker system of the)communication device is configured to enter or be in the first, fullbandwidth mode, when connected via the audio interface to a (one way)audio delivery device. In an embodiment, the (loudspeaker system of the)communication device is configured to enter or be in the second, limitedbandwidth mode, when connected via the audio interface to acommunication device for establishing a (two way) connection to anothercommunication device via a switched network. Alternatively such changesof mod can be initiated via a user interface of the communicationdevice.

Use:

In a further aspect, use of a loudspeaker system as described above inthe detailed description of embodiments, in the drawings. In anembodiment, use in a speakerphone or a mobile (e.g. cellular) telephone(e.g. a SmartPhone) or a headset or a hearing aid is provided.

In an embodiment, the communication device is portable device, e.g. adevice comprising a local energy source, e.g. a battery, e.g. arechargeable battery. In an embodiment, the hearing assistance device isa low power device. The term low power device′ is in the present contexttaken to mean a device whose energy budget is restricted, e.g. becauseit is a portable device, e.g. comprising an energy source, which—withoutbeing exchanged or recharged—is of limited duration (the limitedduration being e.g. of the order of hours or days).

In an embodiment, the communication devices comprise ananalogue-to-digital converter (ADC) to digitize an analogue input with apredefined sampling rate, e.g. 20 kHz. In an embodiment, thecommunication device comprise a digital-to-analogue converter (DAC) toconvert a digital signal to an analogue output signal, e.g. for beingpresented to a user or users via an output transducer.

In an embodiment, the frequency range considered by the communicationdevice from a minimum frequency f_(min) to a maximum frequency f_(max)comprises a part of the typical human audible frequency range from 20 Hzto 20 kHz, e.g. a part of the range from 20 Hz to 12 kHz.

In a particular embodiment, the communication device comprises a voicedetector (VD) for determining whether or not an input signal comprises avoice signal (at a given point in time). Such detector may aid indetermining an appropriate mode of operation of the loudspeaker system.

In an embodiment, the communication device comprises an acoustic (and/ormechanical) feedback suppression system. In an embodiment, thecommunication device further comprises other relevant functionality forthe application in question, e.g. compression, noise reduction, etc.

In an embodiment, the communication device comprises a cellulartelephone or a speakerphone. In an embodiment, the communication devicecomprises a listening device, e.g. an entertainment device, e.g. a musicplayer, e.g. a hearing aid, e.g. a hearing instrument, e.g. a headset,an earphone, an ear protection device or a combination thereof.

Further objects of the application are achieved by the embodimentsdefined in the dependent claims and in the detailed description of theinvention.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well (i.e. to have the meaning “at leastone”), unless expressly stated otherwise. It will be further understoodthat the terms “includes,” “comprises,” “including,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. It will also be understood that when an elementis referred to as being “connected” or “coupled” to another element, itcan be directly connected or coupled to the other element or interveningelements may be present, unless expressly stated otherwise. Furthermore,“connected” or “coupled” as used herein may include wirelessly connectedor coupled. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. The steps ofany method disclosed herein do not have to be performed in the exactorder disclosed, unless expressly stated otherwise.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will be explained more fully below in connection with apreferred embodiment and with reference to the drawings in which:

FIGS. 1A, 1B and 1C show three exemplary embodiments of a loudspeakersystem according to the present disclosure,

FIGS. 2A and 2B show two exemplary embodiments of an equalizer unit fora loudspeaker system according to the present disclosure,

FIGS. 3A, 3B and 3C schematically illustrate various frequencies relatedto an equalization curve and a transfer function of a loudspeaker unitin relation to the present disclosure,

FIG. 4 schematically illustrates exemplary equalization curves fordifferent volume steps according to the present disclosure,

FIG. 5 shows exemplary resulting frequency response curves for aloudspeaker system according to the present disclosure,

FIGS. 6A and 6B show two application scenarios of embodiment of aspeakerphone comprising a loudspeaker system according to the presentdisclosure,

FIG. 7 shows a second embodiment of a speakerphone comprising aloudspeaker system according to the present disclosure, and

FIGS. 8A and 8B show cross-sections of a speaker phone that mayadvantageously include a loudspeaker system according to the presentdisclosure.

The figures are schematic and simplified for clarity, and they just showdetails which are essential to the understanding of the disclosure,while other details are left out.

Further scope of applicability of the present disclosure will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the disclosure, aregiven by way of illustration only. Other embodiments may become apparentto those skilled in the art from the following detailed description.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1A and 1B show three exemplary embodiments of a loudspeaker systemLSS according to the present disclosure. FIG. 1A shows a loudspeakersystem LSS an input unit IU providing an electric input audio signal eINbased on input signal IN. Input signal IN may e.g. be an acoustic signalfrom the environment (in which case input unit IU comprises amicrophone), or an electric signal received from a component of theloudspeaker system or from another device, or a mixture thereof. Theinput unit IU comprises an audio interface. The input signal IN may (incase it is an electric signal) be an analogue signal (e.g. an audiosignal from an audio jack interface) or a digital signal (e.g. an audiosignal from a USB audio interface). The input unit IU may e.g. comprisean analogue to digital converter (ADC) to convert an analogue electricsignal to a digital electric signal (using an appropriate audio samplingfrequency, e.g. 20 kHz). The loudspeaker system LSS further comprises anequalization unit EQ for modifying the electric input audio signal eIN(or a processed version thereof, cf. e.g. FIG. 1B, 1C) in dependence onfrequency and to provide an equalized electric audio signal eINeqaccording to a predefined equalization function. The equalization unitEQ is described in FIGS. 1B and 1C to work in the digital domain (cf.digital signals eIN2/eINeq/eINeq1/eINeq2). The equalization unit may,however, in an embodiment work in the analogue domain. The loudspeakersystem LSS further comprises a loudspeaker unit SPK for converting theequalized electric audio signal eINeq (or a processed version thereof,cf. e.g. FIG. 1B, 1C) to an acoustic output sound signal OUT Theloudspeaker unit SPK may alternatively be a mechanical vibrator of abone anchored hearing device. The loudspeaker system LSS furthercomprises a user interface for modifying a volume level of the outputsound signal OUT in a multitude of steps V₀, V₁, . . . , V_(N), aspecific step being indicated by control signal VOL. In a particularmode of operation of the loudspeaker system LSS, the equalization unitEQ is configured to apply a specific equalization function EQ₀, EQ₁, . .. , EQ_(N) to the electric input audio signal in each of said multitudeof steps V₀, V₁, . . . , V_(N) of the volume level requested via theuser interface UI. The loudspeaker system LSS comprises predefinedequalization functions EQ₀, EQ₁, . . . , EQ_(N) each indicating apredefined frequency dependent gain (e.g. attenuation) to be applied tothe input audio signal when a corresponding volume V₀, V₁, . . . , V_(N)is requested. In other words, corresponding sets of volume setting andequalization function (V_(i), EQ_(i)) is available to the loudspeakersystem LSS. The loudspeaker system LSS is configured to operate in atleast two modes of operation, a first mode and a second mode, whereinthe first mode is a full bandwidth mode, wherein a reproduction of musicor other broadband audio signal is aimed at. The full bandwidth mode isthe mode that is associated with equalization curves (denoted EQ₀-EQ₈)in FIG. 4 and resulting frequency response curves (denoted VOL₀-VOL₈) inFIG. 5.

FIG. 1B illustrates a further embodiment of the loudspeaker system LSS.The embodiment of FIG. 1B contains the same elements as shown anddescribed in connection with FIG. 1A. The embodiment of FIG. 1B furthercomprises an intermediate ‘other’ processing unit OP1 between the inputunit IU and the equalization unit EQ. The processing unit OP1 isconfigured to provide normalization of the digital input audio signaleIN1 and to provide a normalized input audio signal eIN2. Thisfunctionality may e.g. in practice form part of the input unit IU. Thedigitized input audio signal eIN1 may be provided in a variety ofvoltage levels. The processing unit OP1 ‘normalizes’ these voltagelevels to the appropriate level of the loudspeaker system (consideringits power supply voltage, component specifications, etc.). The role ofthe equalization unit EQ is in general to attenuate the normalized inputsignal to a varying degree (depending on frequency and volume level (andmode of operation)). Other processing may be included in OP1. Theequalization unit EQ. receives the normalized (and optionally furtherprocessed) input audio signal and provides as an output an equalizedsignal eINeq (in dependence of a volume control signal VOL received fromthe user interface UI and of a mode control signal MOD received fromcontrol unit CNT). The control unit CNT is configured to monitor theinput unit IU and based thereon to decide which mode of operation theloudspeaker system LSS is intended to operate in (e.g. based on the typeof signal IN received by the input unit IU or by a control signalreceived via the audio interface of the input unit IU). The relevantmode is indicated by mode control signal MOD. The embodiment of FIG. 1Bfurther comprises a further intermediate ‘other’ processing unit OP2, adigital to analogue converter DAC, and an amplifier unit AMP between theequalization unit EQ and the speaker unit SPK. The processing unit OP2is configured to provide optional further processing of the equalizedaudio input signal eINeq (e.g. to apply digital gain, noise reduction orcompression, if relevant) and to provide processed digital output signaldO. The digital to analogue converter DAC (e.g. a sigma-delta converter)converts the digital output signal dO to an analogue output signal aO1.The amplifier unit AMP amplifies analogue output signal aO1 and providesamplified analogue output signal aO2 to loudspeaker unit SPK.

FIG. 1C illustrates a further embodiment of the loudspeaker system LSS.The embodiment of FIG. 1C contains the same elements as shown anddescribed in connection with FIG. 1B. The embodiment of FIG. 1Cillustrates an embodiment where the input unit IU comprises twodifferent audio interfaces, a) a digital audio interface (e.g. an audioUSB interface), where a digital electric input audio signal dIN can bereceived from another device (e.g. a computer, cf. e.g. PC in FIG. 6B),and b) an analogue audio interface (e.g. an audio jack interface), wherean analogue electric input audio signal aIN can be received from anotherdevice (e.g. an entertainment device, cf. e.g. Music player in FIG. 6B).The loudspeaker system LSS further comprises an analogue to digitalconverter ADC to digitize the analogue electric input audio signal aINbefore it enters the input unit IU. In the embodiment of FIG. 1C, theuser interface and control unit (UI and CNT, respectively, of theembodiment of FIG. 1B) are integrated in user interface-control unitUI-CNT, which is configured to receive inputs from a user as well as toextract relevant information from the audio interfaces of the input unitIU, and based thereon (signal MON) to generate control signals MOD andVOL to control equalization unit EQV. The equalization unit EQ of theembodiment of FIG. 1B is in the embodiment of FIG. 1C divided into twofunctional units EQV and EQS. EQV provides a volume (and mode) dependentequalization of normalized input audio signal eIN2 and provides a firstequalized input signal eINeq1 to ‘static’ equalization unit EQS.Equalization unit EQS is configured to provide an equalization of theinput signal that is NOT volume dependent, i.e. which is the same forall equalization function EQ_(i), i=0, 1, 2, . . . , N. Such volumeindependent equalization may e.g. account for (‘clean up’) (minor)deviations of the frequency response curve from an ideal response in theintermediate frequency range (where it is normally relatively flat). The‘static’ equalization unit EQS provides a second equalized input signaleINeq2 to processing unit OP2. The order of the equalization blocks EQVand EQS may be swapped.

FIGS. 2A and 2B show two exemplary embodiments of an equalizer unit fora loudspeaker system according to the present disclosure. FIG. 2A showsan equalization unit EQ as discussed in connection with FIG. 1, e.g. avolume (and mode) dependent equalization unit EQV providing a firstequalized input signal eINeq1 based on normalized input audio signaleIN2 as shown in FIG. 1C. The equalization units of FIG. 2 may or maynot include the static part described in connection with FIG. 1C (unitEQS). FIG. 2A illustrates an embodiment of an equalization unit EQVwherein a separate path for each equalization function (EQ_(i)-M_(x),i=0, 1, 2, . . . , N, and x=1, 2, where N+1 is the number of volumesteps and 2 is the number of modes of operation (which may be 1 orlarger than 2) exists and an appropriate one is chosen in selector unitSEL based on control input signals MOD (current detected or requestedmode of operation) and VOL (current requested volume setting). Theblocks EQ_(i)-M_(x) may be implemented as separate fixed filters eachworking on the same input signal eIN2 and providing a uniqueequalization (attenuation) of the input signal depending on i, x (volumeand mode), a corresponding one being selected as output eINeq1 based oncontrol inputs MOD, VOL.

FIG. 2B illustrates an alternative implementation of the equalizationunit EQ. In the embodiment of FIG. 2B, the equalization unit EQVcomprises a memory storing equalization functions (e.g. in the form offilter coefficients of a variable filter) for each of the 2Nequalization functions (EQ_(i)-M_(x), i=0, 1, 2, . . . , N, and x=1, 2)to be implemented by the loudspeaker system LSS in question. Thenormalized input audio signal eIN2 is fed to a variable filter, here adigital IIR filter, and appropriate filter coefficients are retrievedfrom the memory and applied to the variable filter according to thecurrent requested volume setting and mode of operation. A resulting(first) equalized (input) signal eINeq1 is thereby provided. Otherfilters than a digital IIR filter may be used (e.g. a digital FIR filteror an analogue filter).

FIGS. 3A, 3B, and 3C schematically illustrate various frequenciesrelated to an equalization curve and a transfer function of aloudspeaker unit in relation to the present disclosure.

FIG. 3A illustrates a frequency range of operation of the loudspeakersystem (or a communication device that it forms part of). The system isconfigured to operate in an audio frequency range between a minimumfrequency f_(min) and a maximum frequency f_(max). In an embodiment, theminimum frequency f_(min) is smaller than 50 Hz. In an embodiment, themaximum frequency f_(max) is larger than 4 kHz, e.g. larger than 8 kHz.The frequency of operation is divided into a Low frequency region, aMedium frequency region and a High frequency region, separated bythreshold frequencies f_(LF,th) and f_(LF,th).

FIG. 3B illustrates an exemplary (schematic) equalization curve todefine relevant frequencies. The frequencies f₂ and f₃ correspond inprinciple to the above defined threshold frequencies f_(LF,th) andf_(LF,th). In the equalization functions EQ₀-EQ_(N) of the presentdisclosure, frequencies f₂ and f₃ may be different for differentfunctions (and thus not be identical to the respective thresholdfrequencies f_(LF,th) and f_(LF,th)), but will typically not deviatemuch and be close to the threshold frequencies. Frequency f₁ may bedetermined based on a subjective criterion and/or a power consumptioncriterion, and/or an amplifier voltage and/or a speaker displacement.Frequency f₁ may vary from equalization function to equalizationfunction, and may (for some equalization functions, if possible)coincide with the minimum frequency of operation f_(min). The same isthe case for frequency f₄.

Each specific equalization function defines a low frequency thresholdfrequency f₂ (˜f_(LF,th)) and a high frequency threshold frequency f₃(˜f_(HF,th)) defining respective low, medium and high frequency regions(for that equalization function), wherein the attenuation in the mediumfrequency region between said low frequency and high frequency thresholdfrequencies (f₂, f₃) is larger than the attenuation in the low frequencyregion below said low frequency threshold frequency (f₂). The frequencyf₁ is smaller than the low frequency threshold frequency f₂.Correspondingly, the frequency f₄ is larger than the high frequencythreshold frequency f₃. The loudspeaker system is configured to operatein an audio frequency range between a minimum frequency f_(min) (e.g.≦50 Hz) and a maximum frequency f_(max). (e.g. ≧4 kHz).

The course of the equalization curves in frequency ranges f₁-f₂ andf₃-f₄ are intended to compensate for the deviation of the frequencyresponse of the loudspeaker unit at low and high frequencies,respectively (below f_(LFcut) and above f_(HFcut), respectively, cf.FIG. 3C). The attenuation of the exemplary equalization function of FIG.2B is shown to increase in the low frequency region between f₁ and f₂from the medium frequency range level L(f₂) at f₂ to a minimumattenuation level L(f₁) at f₁. Correspondingly, the attenuation of theexemplary equalization function of FIG. 2B is shown to increase in thehigh frequency region between f₃ and f₄ from the medium frequency rangelevel L(f₃) at f₃ to an attenuation level L(f₄) at f₄. In the schematicgraph EQ_(app)(f) the course between indicated neighboring frequenciesf_(p), f_(q) (e.g. between f₁ and f₂) is linear. In practice, it maydeviate from linearity, either deliberately, or due to finite filtersizes and non-linearities of components (as schematically indicated bygraph EQ(f)).

FIG. 2C schematically illustrates a frequency transfer function(Amplitude in dB vs. frequency f) of a loudspeaker unit. A typicalloudspeaker unit has a medium frequency range providing a substantiallyflat transfer function H(f) for frequencies in the medium frequencyrange between first (f_(LFcut)) and second (f_(HFcut)) frequencies(f_(LFcut)<f_(HFcut))). Below a low frequency cut-off frequency(f_(LFcut)), the frequency response of the loudspeaker unit rolls off(e.g. ˜12 dB/octave). In other words, the loudspeaker unit will—otherthings being equal—play low frequency sounds (below f_(LFcut)) at alower output level than sounds in the medium frequency range. The sameis to a certain extent true for sound signals above a high frequencycut-off frequency (f_(HFcut)). Depending on the loudspeaker unit inquestion, the low frequency cut-off frequency (f_(LFcut)) is smallerthan 500 Hz, e.g. smaller than 400 Hz, e.g. in the range from 200 Hz to400 Hz. Correspondingly, he high frequency cut-off frequency (f_(HFcut))depends on the loudspeaker unit in question. Preferably, it is largerthan 4 kHz, e.g. larger than 8 kHz, e.g. larger than 12 kHz, e.g. in therange from 4 kHz to 10 kHz. An idealized graph H_(app)(f) and a(schematic) real transfer function graph H(f) are indicated in FIG. 2C.The idealized (piecewise linear) graph H_(app)(f) may e.g. be the resultof a pre-shaping (cf. static equalization unit EQS) of the real transferfunction H(f), as discussed in connection with FIG. 1C above.

Preferably, the low frequency threshold frequency f₂(i) of a specificequalization function EQ_(i) is dependent on the low frequency cut-offfrequency f_(LFcut) of the loudspeaker unit. Correspondingly, the highfrequency threshold frequency f₃(i) of a specific equalization functionEQ_(i), is dependent on the high frequency cut-off frequency f_(HFcut)of the loudspeaker unit.

It should be noted, that the present scheme of volume (and mode)dependent equalization may also be applied to other (non-ideal)deviations of a loudspeaker transfer function from ideality, e.g. a dipin the transfer function at medium frequencies.

FIG. 4 shows exemplary equalization curves EQ(f) (EQ0, EQ1, . . . , EQ8;here the number of volume steps is 9) versus frequency f, for differentvolume steps (V0, V1, . . . , V8) according to the present disclosure.The equalization curves generally have the form as described inconnection with FIG. 3B. The graphs show the Magnitude in dB of theattenuation at different volume levels V_(i). The distance between twoequalization curves in the intermediate range between f₂ and f₃ areindicated to be identical (indicating the same, constant step height (indB) between individual volume steps, e.g. of the order of 3 dB or 4 dB).This need not be the case, however. The steps may vary (e.g. to decreasewith increasing volume level, or vice versa) depending on theapplication. The (maximum) levels of attenuation (minimum levels L_(min)(EQ_(i))) of the intermediate frequency range (between frequencies f₂and f₃) are indicated for each equalization curve EQ_(i) and volume stepV_(i). In the low frequency region between frequencies f₁ and f₂, theattenuation for each equalization curve EQ_(i) decreases linearly (in alogarithmic representation) for decreasing frequencies between therespective maximum levels of attenuation (L_(min)(EQ_(i)) to a minimumlevel of attenuation (L_(max)), e.g. corresponding to no attenuation (0dB), i.e. exploiting the transfer function of the loudspeaker unit toits maximum. In an embodiment, the difference between minimum andmaximum attenuation in the intermediate frequency range (f₂-f₃) issmaller than or equal to 40 dB, e.g. smaller than or equal to 30 dB. Theequalization curves EQ_(i) are generally shown to end on a constantattenuation level in the lowest and highest frequency ranges betweenf_(min) and f₁ and between f₄ and f_(max), respectively. This need notbe the case however, as indicated in the high frequency region for theequalization functions EQ₀, EQ₁, EQ₂ corresponding to the lowest volumesettings V₀, V₁, V₂ where the attenuation decreases (at different rates)for increasing frequency in the high frequency region between f₄ andf_(max).

The low and high frequency threshold frequencies f₁ and f₂ are hereassumed to be identical for all equalization curves, and equal the lowand high frequency cut-off frequencies (f_(LFcut) and f_(HFcut)) of theloudspeaker unit, respectively, s indicated below the frequency axis inFIG. 4. It is also indicated that the low and high frequency thresholdfrequencies f₁ and f₂ are identical to the respective low and highfrequency threshold frequencies (f_(LF,th) and f_(HF,th)) of the FIG. 3Adefining the 3 frequency regions of the operating frequency rangebetween a minimum f_(min) and a maximum f_(max) (audio) frequency of theloudspeaker system.

FIG. 5 shows exemplary resulting frequency response curves RFR(f,VOL)for a loudspeaker system according to the present disclosure. The graphsschematically show Magnitude (in dB) versus frequency f for a number ofvolume settings VOL_(E) (i=0, 1, . . . , 8). The resulting frequencyresponse curves are assumed to result from the equalization curves ofFIG. 4 and a frequency response curve or the loudspeaker unit (asexemplified in FIG. 3C).

The (maximum) output levels L(VOL_(i))) of the intermediate frequencyrange (between frequencies f₂ and f₃) are indicated for each volume stepVOL_(i).

The volume step dependent equalizer of the present disclosure mayaddress two issues:

-   -   Primarily: When decreasing the volume linearly over frequency        one misses the opportunity to exploit the speaker capabilities        fully in the low frequency (LF) region at low playback levels.    -   Secondarily: When decreasing the volume linearly over frequency        the tonal balance is perceived changed due to well known        psychoacoustic loudness effects.

The present scheme addresses mainly the first but may to some extendalso address the second issue by utilizing separate EQ-curves for eachvolume step. This is e.g. the reason for the LF-boost in the lowestlevel and the HF-boost the 3 lowest volume levels, as illustrated inFIG. 5.

The upper curve (VOL₈) describes a flat speaker response with a LF cutoff point at f₂ (e.g. corresponding to approximately 325 Hz). The othercurves (VOL₂-VOL₇) exhibit the same course, only that the follow thedecay of the curve corresponding to maximum volume (no attenuation,VOL₈) below a cutoff frequency f_(c). (e.g. around 75 Hz).Alternatively, however, the cutoff point at f₂ may be gradually loweredin frequency with decreasing volume level until it at the lowest volumestep reaches f_(c). This can be achieved by extending the levelL(VOL_(i)) i=1-7) of the intermediate frequency region in the frequencyrange below f₂ until it reaches the boundary curve corresponding to VOL₈(bold line).

At the very lowest step (VOL₀) an additional bass boost is appliedmaking the response peak around f_(c) (e.g. 75-100 Hz). This can beconsidered as a small loudness compensation.

To enable as loud as possible playback within the available maximumvoltage swing, no high frequency boost is applied at the highest volumestep (cf. FIG. 4). This boost is introduced at the second highest volumestep and is kept all the way down to the lowest volume step (cf. rangef₃-f₄ in FIG. 4). At the three lowest volume steps (VOL₀, VOL₁, VOL₂), afurther, gradual HF-boost is implemented (cf. range f₄-f_(max) in FIG.4). This can be considered a small loudness compensation.

In an embodiment, the above scheme is implemented in the digital domain.Preferably, a full scale input is provided (by normalization). In anembodiment, no dynamic processing is used to boost small signal inputlevels (as e.g. proposed in WO9318626A1).

The present scheme is preferably used in a first mode of operation wheremusic or multimedia playback is to be reproduced by the loudspeakersystem (e.g. forming part of a speakerphone). A similar function can beused for playback during a second mode of operation where communicationis highlighted (e.g. via a telephone line), but with differentequalization functions. In general, it is anticipated that there is nosubstantial benefit from a bass boost in e.g. telephone conversation.

FIGS. 6A and 6B show two application scenarios of an embodiment of acommunication device CD, here a speakerphone, comprising a loudspeakersystem according to the present disclosure. The communication device(CD) is configured to be separately or simultaneously connected to acomputer PC and a cellular telephone CellPh.

FIG. 6 shows an embodiment of a communication device (CD) comprising twowired audio interfaces to other devices, a) a wireless telephone(CellPh, e.g. a cellphone, e.g. a Smartphone, FIG. 6A) or a one-wayaudio delivery device (Music player in FIG. 6B), and b) a computer (PC,e.g. a PC). The audio interface to the computer (PC) comprises an USB(audio) interface including a cable and an USB-connector (PC-Con) fordirectly connecting the communication device to the computer andallowing two-way audio to be exchanged between the communication deviceCD and the computer. The audio interface to the wireless telephone(CellPh) comprises a cable and a phone connector (PhCon) for directlyconnecting the communication device to the computer and allowing two-wayaudio to be exchanged between the communication device and the computer.Preferably, the phone connector has the function of a headset connection(to transfer the audio input capability of the wireless telephone to themicrophone(s) (MIC) of the communication device, and to transfer theaudio output of the wireless telephone to the loudspeaker(s) (SPK) ofthe communication device. The communication device (CD) comprises anumber of activation elements (B1, B2, B3), e.g. push buttons (oralternatively a touch sensitive display) allowing the control offunctions of the communication device and/or devices connected to thecommunication device. Preferably, one of the activation elements (e.g.B1) is configured to allow connection (hook-off, answer call) and/ordis-connection (hook-on, terminate call) of the wireless telephone(CellPh) connected to the communication device via the phone connector(PhCon). Preferably, one of the activation elements (e.g. B2) isconfigured to allow a user to control the volume of the loudspeakeroutput. Preferably, one of the activation elements (e.g. B3) isconfigured to allow a user to control a mode of operation of theloudspeaker system of the communication device.

The scenario shown in FIG. 6A illustrates a teleconference between users(U1, U2) in the vicinity of the communication device (CD) and users(RU1, RU2, and RU3) at two (different) remote locations. Remote user RU1is connected to the communication device (CD) via wireless telephone(CellPh) and wireless connection WL1 to a network (NET). Remote usersRU2, RU3 are connected to the communication device (CD) via computer(PC) and wired connection WI1 to a network (NET). The scenario shown inFIG. 6A corresponds to a second, Limited bandwidth mode of operation ofthe loudspeaker system.

FIG. 6B illustrates a slightly different scenario than FIG. 6A. FIG. 6Billustrates the reception (and optional mixing) of audio signals fromthe various audio delivery devices (Music player and PC) connected tothe communication device (CD). The scenario shown in FIG. 6B correspondsto a first, Full bandwidth mode of operation of the loudspeaker system.The communication device (CD) comprises two (two-way) audio interfacesembodied in I/O units IU1/OU1 and IU2/OU2, respectively. T

The communication device of FIG. 6B comprises a loudspeaker signal path(SSP), a microphone signal path (MSP), and a control unit (CONT) fordynamically controlling signal processing of the two signal paths. Theloudspeaker signal path (SSP) comprises receiver units (IU1, IU2) forreceiving an electric signal from a connected device and providing it asan electric received input signal (S-IN1, SIN2), an SSP-signalprocessing unit (G1) for processing (including equalizing) the electricreceived input signal (S-IN1, SIN2) and providing a processed outputsignal (S-OUT), and a loudspeaker unit (SPK) operationally connected toeach other and configured to convert the processed output signal (S-OUT)to an acoustic sound signal (OS) originating from the signal received bythe receiver unit (IU1, IU2). The microphone signal path (MSP) furthercomprises a selector-mixing unit (SEL-MIX) for selecting one of the twoinputs audio signals (or mixing them) and providing a resulting signalS-IN to the SSP-signal processing unit (G1). The microphone signal path(MSP) comprises a microphone unit (MIC) for converting an acoustic inputsound (IS) to an electric microphone input signal (M-IN), an MSP-signalprocessing unit (G2) for processing the electric microphone input signal(M-IN) and providing a processed output signal (M-OUT), and respectivetransmitter units (OU1, OU2) operationally connected to each other andconfigured to transmit the processed signal (M-OUT) originating from aninput sound (IS) picked up by the microphone unit (MIC) to the connecteddevice (if relevant possible). The control unit (CONT) is configured todynamically control the processing of the SSP- and MSP-signal processingunits (G1 and G2, respectively), including mode selection, equalizationin the SSP path, and optionally muting the microphone unit (MIC) of theMSP path (via control output signals G1 c G2 c, and MUTE, respectively,based on control input signal MOD and VOL from the user interface UIand/or on control inputs signals mod1 and mod2 from the audio interfacesIU1/OU1, IU2/OU2, respectively).

The loudspeaker signal path (SSP) is divided in two (IU1, IU2) forreceiving input signals from the respective audio devices (Music playerand PC). Likewise, the microphone signal path (MSP) is divided in two(OU1, OU2) for transmitting output signals to the respective audiodevices (Music player (not relevant) and PC). One-way and two-way audioconnections between the communication device (units IU1, IU2 and OU1,OU2) and two the audio devices (here Music player and PC) can beestablished via jack connector (JckCon) and cable (Jck-I-O), and USBconnector (PC-Con) and cable (PC-I-O), respectively.

FIG. 7 shows a second embodiment of a communication device CD (here aspeakerphone) comprising a loudspeaker system according to the presentdisclosure. The unit and functionality is identical to the one describedin connection with FIG. 6B (and may thus represent a relevant mode ofoperation, where the volume dependent equalization according to thepresent disclosure is advantageously applied). In the embodiment of FIG.7, the audio interfaces are included in I/O control unit I/O-CNT, whichreceives input signals from the devices connected to the respectiveaudio interfaces and transmit an output signal to the connected devices,if relevant. In a listening mode, where music or other broadband audiosignals are received from one or both audio delivery devices (Musicplayer, and PC), it is assumed that, no audio signal is transmitted fromthe communication device (CD) to the connected audio delivery devices.The listening mode may hence be equal to the previously discussed ‘fullbandwidth mode’. The I/O control unit I/O-CNT, is connected to powercontrol unit PWR-C and a battery BAT. The power control unit PWR-Creceives signal PWR from the I/O control unit I/O-CNT enabling adetection of a possible power supply signal from the audio interfaceand—if such power supply is present—to initiate a recharging of arechargeable battery (BAT), if relevant. It further provides controlsignal CHc to the control unit indicating whether the current powersupply is based on a remote source (e.g. received via the audiointerface or via a mains supply) or whether the local energy source(BAT) is currently used. Such information can be used in the controlunit CONT to decide on an appropriate mode of operation in general, butalso regarding the volume dependent equalization. A specific set ofvolume dependent equalization functions for a battery mode and for anexternal power supply mode may be defined and the appropriate sets ofparameters (e.g. filter coefficients, cf. FIG. 2B) for implementing therespective equalization functions may be stored in the communicationdevice.

FIGS. 8A and 8B show (perspective) cross-sections of a speaker phone(CD) that may advantageously include a loudspeaker system according tothe present disclosure. FIGS. 8A and 8B are identical apart from FIG. 8Abeing a shaded version and FIG. 8B a line drawing. The speaker phonecomprises a centrally located loudspeaker unit (SPK) having a speakercone (SPK-CON) of diameter SPK-DIM, cf. FIG. 8A. The speaker diametercan have any size appropriate for the application in question.Preferably, the diameter is smaller than 1 m. In a speakerphone asdepicted in FIG. 8, a diameter of less than 0.2 m, such as less than0.15 m is relevant. The maximum dimension of the communication device(CD, here speaker phone) in FIG. 8 is termed CD-DIM (cf. FIG. 8B). In aspeakerphone as depicted in FIG. 8, a maximum device dimension of lessthan 0.4 m, such as less than 0.25 m is relevant. The communicationdevice comprises a user interface UI in the form of a centrally locatedactivation element (push button), e.g. for changing a mode of operationof the device (or for activating an on or an off state, etc.)

The invention is defined by the features of the independent claim(s).Preferred embodiments are defined in the dependent claims. Any referencenumerals in the claims are intended to be non-limiting for their scope.

Some preferred embodiments have been shown in the foregoing, but itshould be stressed that the invention is not limited to these, but maybe embodied in other ways within the subject-matter defined in thefollowing claims and equivalents thereof.

REFERENCES

-   [Haykin; 2001] S. Haykin, Adaptive filter theory (Fourth Edition),    Prentice Hall International Inc., 2001.-   WO9318626A1

1. A loudspeaker system comprising a) an input unit providing anelectric input audio signal; b) an equalization unit for modifying saidelectric input audio signal or a processed version thereof in dependenceon frequency and to provide an equalized electric audio signal accordingto a predefined equalization function, and c) a loudspeaker unit forconverting said equalized electric audio signal or a processed versionthereof to an acoustic output sound signal, d) a user interface formodifying a volume level of said output sound signal in a multitude ofsteps V₀, V₁, . . . , V_(N), e) an I/O control unit for monitoring aconnected interface to the loudspeaker system, wherein the equalizationunit is configured to apply a specific equalization function EQ₀, EQ₁, .. . , EQ_(N) to the electric input audio signal in each of saidmultitude of steps V₀, V₁, . . . , V_(N) of the volume level, and theloudspeaker system is configured to operate in at least two modes ofoperation, a first mode operating in a full bandwidth mode and a secondmode operating in a limited bandwidth, and the loudspeaker system isfurther configured to automatically be brought in to either the first orsecond mode depending on the monitored interface.
 2. A loudspeakersystem according to claim 1 wherein the equalization unit is configuredto provide that at least two of said specific equalization functionsEQ₀, EQ₁, . . . , EQ_(N) are different.
 3. A loudspeaker systemaccording to claim 1 wherein the equalization unit is configured toprovide that each specific equalization function defines a frequencydependent attenuation of the electric input audio signal.
 4. Aloudspeaker system according to claim 1 wherein each specificequalization function defines a low frequency threshold frequency f₂,and a high frequency threshold frequency f₃, defining respective low,medium and high frequency regions, wherein the attenuation in the mediumfrequency region between said low frequency and high frequency thresholdfrequencies is larger than the attenuation in the low frequency regionbelow said low frequency threshold frequency.
 5. A loudspeaker systemaccording to claim 1, further configured to provide: that each specificequalization function EQ_(i), i=0, 1, 2, . . . , N, is applied toelectric audio signal when the corresponding respective step V_(i), i=0,1, 2, . . . , N, of the volume level is selected, where increasing icorresponds to increasing volume, that each equalization functionEQ_(i)(f) represents a specific frequency dependent attenuationEQ_(i)(f), and that the attenuation of an equalization functionEQ_(i)(f) is smaller than the attenuation of an equalization functionEQ_(j)(f) for all frequencies in the range from an LF frequency f_(LF)to a HF frequency f_(HF), if i is larger than j.
 6. A loudspeaker systemaccording to claim 4 configured to provide that the low frequencythreshold frequency f₂ of a specific equalization function is dependenton a low frequency cut-off frequency f_(LFcut) of the loudspeaker unit.7. A loudspeaker system according to claim 1 wherein a specificequalization function is implemented by a filter.
 8. A loudspeakersystem according to claim 7 comprising a memory wherein predefined setsof filter coefficients for implementing specific equalization functionsare stored.
 9. A loudspeaker system according to claim 1 configured towork under power constraints in that the maximum voltage swing that canbe applied to the loudspeaker unit is limited by one or more of thefollowing a) the available power in the loudspeaker system, b) a maximumamplifier output, and c) specifications of the loudspeaker unit.
 10. Aloudspeaker system according to claim 1, wherein the loudspeaker unithas a maximum dimension that is smaller than or equal to 1 m.
 11. Aloudspeaker system according to claim 1 comprising a wired or wirelessaudio interface to another device.
 12. A loudspeaker system according toclaim 1 configured to automatically be energized by another device orsystem, when connected to such other device or system via an audiointerface providing power.
 13. A loudspeaker system according to claim 1configured to automatically be brought in a particular mode of operationdepending on the currently connected audio interfaces.
 14. Acommunication device comprising a loudspeaker system according toclaim
 1. 15. A communication device according to claim 14, furthercomprising: a first microphone signal path including a microphone unit,a first signal processing unit, and a transmitter unit, said microphoneunit, first signal processing unit, and transmitter unit beingoperationally connected to each other and configured to transmit aprocessed signal originating from an input sound picked up by themicrophone, and a second loudspeaker signal path including a receiverunit, a second signal processing unit, and a second loudspeaker unit,said receiver unit, second signal processing unit, and secondloudspeaker unit being operationally connected to each other andconfigured to provide an acoustic sound signal originating from a signalreceived by the receiver unit.
 16. A communication device according toclaim 14 comprising at least one audio interface to a switched networkand at least one audio interface to an audio delivery device.
 17. Aspeakerphone, comprising a loudspeaker system that includes an inputunit providing an electric input audio signal; an equalization unit formodifying said electric input audio signal or a processed versionthereof in dependence on frequency and to provide an equalized electricaudio signal according to a predefined equalization function; aloudspeaker unit for converting said equalized electric audio signal ora processed version thereof to an acoustic output sound signal; and auser interface for modifying a volume level of said output sound signalin a multitude of steps V₀, V₁, . . . , V_(N); and an I/O control unitconfigured to monitor a connected interface to the loudspeaker, whereinthe equalization unit is configured to apply a specific predefinedstatic equalization function EQ₀, EQ₁, . . . , EQ_(N) to the electricinput audio signal in each of said multitude of steps V₀, V₁, . . . ,V_(N) of the volume level, and the loudspeaker system is configured tooperate in at least two modes of operation, a first mode operating in afull bandwidth and a second mode operating in a limited bandwidth, andthe loudspeaker system is further configured to automatically be broughtin to either the first or second mode depending on the monitoredinterface.